The present invention relates to an improved two-phase process for carrying out a continuous reaction (such as dimerisation, co-dimerisation, oligomerisation or metathesis of olefins) on an organic feed, using a catalyst which contains at least one catalytic clement, dissolved in a non-aqueous ionic medium which is not or is only slightly miscible with the olefins. In other words, it relates to a process for carrying out a two-phase catalyzed reaction. The invention also relates to a unit for carrying out the process.
As described above, a two-phase system has the advantage of using the catalyst better than using a single-phase, homogeneous system. However, continuous economic implementation of a two-phase system poses a certain number of problems, such as interference with the catalyst and with the polar phase by trace impurities contained in the feeds. Such impurities are water, alcohols, ethers, nitrogen-containing compounds and sulphur-containing compounds. They react with the catalyst-polar phase complex.
The process of the invention consists of circulating a counter-current of feed and polar phase in at least two treatment loops. This results in a pre-treatment of the feed in the first loop by used catalytic composition, i.e., that which has lost the majority of its activity, the used catalytic composition originating from the second loop, and then being withdrawn from the process. This implementation reduces consumption of the catalyst-polar phase system, avoids the need for a section for eliminating the transition element and enables the catalyst to be treated off-site.
The process of the invention is a process for carrying out a reaction on an organic feed, in the presence of a polar phase containing at least one catalytic composition resulting from mixing: at least one non-aqueous ionic medium which is not or is only slightly miscible with the organic phase; at least one compound of a catalytic element; and optionally at least one co-catalyst.
In the process of the invention, the feed to be treated and the non-aqueous medium circulate as a counter-current between at least two treatment loops, each loop comprising at least one reaction zone connected to at least one zone for separating the organic and polar phases, the feed to be treated being supplied to the reaction zone of the first loop and fresh non-aqueous ionic medium, i.e., as yet unused, being introduced to the reaction zone in the second or final loop. The other constituent(s) of the catalytic composition can be introduced to any part of the process. The polar phase separated in the separation zone of the second loop or from each of the subsequent loops is sent to the reaction zone of the first loop or respectively the preceding loop, while the organic phase separated in the separation zone of the first loop or its subsequent loops is sent to the reaction zone of the second loop or respectively its subsequent loop. The organic phase obtained from the separation zone of the final loop and the polar phase obtained from the separation zone of the first loop are withdrawn from the process.
In a preferred variation, a portion of the reaction medium from one reaction zone is withdrawn from one part of said zone for re-injection into said zone.
Advantageously, at least a portion of the polar phase withdrawn from one separation zone of a loop is recycled to the reaction zone of the same loop.
Preferably, said fresh non-aqueous ionic medium also comprises at least a portion of at least one constituent of the catalytic composition. In that case, advantageously, the fresh non-aqueous ionic medium introduced to part of the final loop also comprises at least one transition element compound.
Preferably again, at least a portion of at least one constituent of the catalytic composition is introduced to part of the reaction zone of the first loop. Again advantageously, fresh co-catalyst is introduced into the reaction zone of the first loop.
In one implementation of the invention, a fresh catalytic composition comprising fresh non-aqueous ionic medium and at least one transition element compound and optionally at least one co-catalyst are introduced into the reaction zone of the last loop.
In the two-loop implementation illustrated below, the process comprises a first and a second treatment loop, each comprising a reaction zone (respectively A1 and A2) connected to a separation zone (respectively B1 and B2),
the feed to be treated is supplied to the first reaction zone A1, also co-catalyst, fresh non-aqueous ionic medium mixed with at least one transition element compound and optionally at least a portion of the co-catalyst being supplied to the second reaction zone A2;
the polar phase separated from separation zone B2 is introduced into the reaction zone A1, while the organic phase separated in separation zone B1 is introduced into reaction zone A2;
the organic phase containing the reaction products separated in separation zone B2 and the used polar phase separated in separation zone B1 being withdrawn from the process.
In one implementation, for example, a portion of the reaction medium is withdrawn from the reaction zone of the second loop, cooled and re-injected into that zone.
The non-aqueous ionic medium comprises at least one salt known as a xe2x80x9cmolten saltxe2x80x9d and preferred salts of the invention have general formula Q+Axe2x88x92 where Axe2x88x92 represents a non co-ordinating or slightly co-ordinating anion. Preferred compounds are those which can form a liquid salt at low temperature, i.e., below 150xc2x0 C. and advantageously at most 80xc2x0 C., preferably below 50xc2x0 C., for example halogenoaluminates, organohalogenoaluminates, halogenogallates, and organohalogenogallates. Q+ represents a quaternary ammonium and/or quaternary phosphonium ion. The quaternary ammonium and/or phosphonium ions preferably have general formulae NR1R2R3R4+ and PR1R2R3R4+ or general formulae R1R2Nxe2x95x90CR3R4+ and R1R2Pxe2x95x90CR3R4+ where R1, R2, R3 and R4, which may be identical or different, represent hydrogen with the exception of the cation NH4+, and preferably a single substituent represents hydrogen, or hydrocarbyl residues containing 1 to 12 carbon atoms, for example saturated or unsaturated alkyl groups, cycloalkyls or aromatics, aryl or aralkyl groups, containing 1 to 12 carbon atoms. The ammonium and/or phosphonium ions can also be derivatives of nitrogen-containing or phosphorus-containing heterocycles containing 1, 2 or 3 nitrogen and/or phosphorous atoms, with general formulae: 
where the cycles are constituted by 4 to 10 atoms, preferably 5 or 6 atoms, R1 and R2 being defined as above. The quaternary ammonium or phosphonium ion can also be, a cation with formula:
R1R2+Nxe2x95x90CR3xe2x80x94R5xe2x80x94R3Cxe2x95x90N+R1R2 
R1R2+Pxe2x95x90CR3xe2x80x94R5xe2x80x94R3Cxe2x95x90P+R1R2 
where R1, R2 and R3, which may be identical or different, are defined as above and R5 represents an alkylene or phenylene residue. The following R1, R2, R3 and R4 groups can be mentioned: methyl, ethyl, propyl, isopropyl, butyl, secondary butyl, tertiary butyl, amyl, methylene, ethylidene, phenyl or benzyl radicals; R5 may be a methylene, ethylene, propylene or phenylene group. The ammonium and/or phosphonium cation is preferably selected from the group formed by N-butylpyridiunium, N-ethylpyridinium, 3-butyl-1-methylimidazolium, diethylpyrazolium, 3-ethyl-1-methylimidazolium, pyridinium, trimethylphenylammonium, 3-ethyl-1-methylimidazolium, and tetrabutylphosphonium.
These salts can be used alone or as a mixture. They act as a solvent.
For dimerisation, co-dimerisation, or oligomerisation, for example, the polar phase of the invention can also comprise a mixture of at least one lithium halide with at least one hydrocarbylaluminium halide (as described in European patent application EP-A-0 753 346).
In a further implementation, it can comprise a mixture of at least one ammonium halide or quaternary pheosphonium halide with at least one aluminium halide and/or at least one hydrocarbylaluminium dihalide (as described in EP-A-0 448 445, French patent FR-A2 2 611 700 and EP-A-0 646 412). Nickel is the preferred catalytic element.
The preferred polar phase of the invention comprises (or advantageously is constituted by) a mixture of at least one aluminium halide or respectively at least one hydrocarbylaluminium halide with at least one quaternary ammonium halide and/or quaternary phosphonium halide, or respectively a lithium halide, and advantageously in a molar ratio of aluminium compound/molten salt which is in the range 1 to 2, preferably 1.1 to 1.6.
The hydrocarbylaluminium halide has general formula Al2XxR6-x where X is chlorine or bromine, R is an alkyl, cycloalkyl, aryl or aralkyl radical comprising 1 to 10, preferably 2 to 6, carbon atoms, x taking the values 2, 3 or 4. They can be used alone or as a mixture. Examples are alkylaluminium chlorides such as ethylaluminium dichloride, isobutylaluminium dichloride, ethylaluminium sesquichloride and diethylaluminium chloride.
The catalytic element (generally a transition metal from groups 6, 8, 9 or 10) is used in the form of a salt such as a carboxylate, acetylacetonate, chloride, bromide, sulphate, nitrate or complexes which these salts form with phosphines, amines, or nitriles. Other compounds may also be suitable.
The concentration of transition metal compound in the polar phase is advantageously in the range 1 mmole per liter to 500 mmoles per liter, preferably in the range 2 to 300 mmoles per liter.
The invention is not limited to the catalytic compositions described above; other compositions may be suitable for dimerisation, co-dimerisation or oligomerisation.
For metathesis, for example, it is possible to use a composition as described in French patent application FR-A-2 715 328, comprising at least one ammonium halide and/or quaternary phosphonium halide mixed with at least one aluminium halide and at least one organometallic aluminium compound. This latter generally has formula Al2XxR3-x where R is a linear or branched alkyl radical containing 2 to 8 carbon atoms, X is chlorine or bromine and x equals 1, 2 or 3. The catalytic element is tungsten or molybdenum (group 6).
Other catalysts may be suitable.
More generally, the catalyst selected is that which is suitable for the desired reaction.
The reaction mixture comprises a hydrocarbon phase constituted by reactants, products and inert constituents, and the polar phase contains the dissolved transition metal complex.
The temperatures at which the reaction and separation are carried out are generally substantially identical and are generally in the range xe2x88x9220xc2x0 C. to +80xc2x0 C., preferably xe2x88x9210xc2x0 C. to +60xc2x0 C., The pressure is sufficient to maintain all of the reactants and constituents of the cuts in the liquid phase, i.e., in the complete absence of a gas phase. The operating conditions are clearly those necessary for carrying out the desired reaction.
The invention also relates to a unit for carrying out the reaction in a non-aqueous ionic medium which is not or is only slightly miscible with olefins, comprising:
at least two reaction zones A1 and A2;
at least two separation zones B1 and B2 for separating the hydrocarbon phase from the polar phase, said zones being connected to the reaction, ones A1 and A2;
at least one conduit 1 for introducing polar phase into reaction zone A2;
at least one conduit 2 for introducing olefin food into reaction zone A1;
at least one conduit 3 for supplying hydrocarbon phase separated in separation zone B1 to reaction zone A2;
at least one conduit 4 for withdrawing hydrocarbon phase separated in separation zone B2;
at least one conduit 5 for sending die polar phase separated in separation zone B2 to reaction zone A1;
at least one conduit 6 for withdrawing used polar phase separated in separation zone B1.
The unit preferably also comprises the following means, taken alone or in combination:
at least one conduit 7 connecting separation zone B2 to reaction zone A2 to recycle the polar phase;
at least one conduit 8 for withdrawing a portion of the reaction medium from zone A2 and re-introducing it to said zone;
at least one conduit 9 for withdrawing a portion of the reaction medium from zone A1 and re-introducing it to said zone;
at least one conduit 10 connecting separation zone B1 to zone A1 for recycling the polar phase;
at least one conduit 11 for introducing the reactants into the unit.
Conduits 8 and 9 advantageously comprise heat exchangers.